1. Technical Field of the Invention
The present invention relates in general to a system and method for communicating data, and in particular for simultaneously communicating data between multiple devices on a shared data bus.
2. Description of Related Art
Different electronics devices communicate data at different rates. Generally, the data rate for a particular device is dependent upon how advanced the device is and upon the rate of data exchange that is required for proper operation of the device. For example, low-cost electronics accessories typically operate at a low data rate and use a simple electrical interface. More advanced accessories, on the other hand, frequently require the use of electrical data buses that can support high data rates.
Many products and systems that incorporate electronic accessories, such as cellular telephones, include a number of interconnected devices, which can have varying levels of complexity. Some of the more complex devices must operate at high data rates while many of the simpler devices are incapable of operating at a high data rate. As a result, such systems or products typically require two or more electrical data buses to support communications with the various devices of the particular system or product, increasing space requirements and cost. The use of multiple data buses also requires a greater number of connector pins on system connectors and processors that control the system or product, which also takes up more space and adds expense.
There is a need, therefore, for a system and method for communicating data to and from both high-speed devices and low-speed devices using a common electrical bus. Such a system and method would reduce the space and the number of connector pins required to interconnect multiple devices having the same or differing data rates. In addition, such a system and method would preferably permit the simultaneous use of the common electrical data bus for both high-speed and low-speed data transfers.
The present invention comprises a method and system for communicating at least two data transfers on a shared data bus. The system includes a simple electronic device that communicates via the shared data bus at a low data rate and a high-speed electronic device that communicates via the shared data bus at a high data rate. Alternatively, two devices can transmit data via the data bus at the same time using the same data rate. Generally, the shared data bus is also connected to a system processor, system connector, and/or other high-speed or low-speed devices.
Communications at the low data rate are conducted by varying a voltage level on the shared data bus within the full voltage swing of the shared data bus. The full voltage swing is divided into at least a low voltage range and a separate high voltage range. A voltage level on the shared data bus that is within the low voltage range represents a first data value, such as a binary value of zero, and a voltage level on the shared data bus that is within the high voltage range represents a second data value, such as a binary value of one. Thus, devices can communicate via the shared data bus at the low data rate by selectively varying the voltage level between at least the low voltage range and the high voltage range.
At the same time as communications at the low data rate are ongoing, communications at the high data rate can also be conducted by varying the voltage level within either the low voltage range or the high voltage range, depending on which data value is currently being transmitted at the low data rate. Accordingly, the low voltage range and the high voltage range are each divided into sub-levels or sub-ranges. Thus, when a device communicating at the low data rate is transmitting the first data value (i.e., within the low voltage range), a high-speed device can simultaneously transmit data at the high data rate by varying the voltage level between sub-levels within the low voltage range. Similarly, when a device communicating at the low data rate is transmitting the second data value (i.e., within the high voltage range), a high-speed device can simultaneously transmit data at the high data rate by varying the voltage level between sub-levels within the high voltage range.